ADTRAN AOS Version R10.1.0 Command Reference Manual page 2658

Command Reference Guide
ipv6 mtu <size>
Use the ipv6 mtu command to specify the maximum transmission unit (MTU) for Internet Protocol
version 6 (IPv6) packets on the interface. Use the no form of this command to return to the default value.
Syntax Description
<size>
Default Values
By default, the MTU of the interface is set to 1280 bytes.
Command History
Release 18.1
Release R10.1.0
Functional Notes
In IPv6, the minimum MTU is 1280 octets. Any link that has an MTU less than 1280 octets must use link
fragmentation and reassembly that is transparent to IPv6 (for example, the Fragmentation Header).
Sources in the IPv6 network are expected to perform path maximum transmission unit (PMTU) discovery
to send packets larger than 1280 octets. PMTU works in the following manner: First, the sending node
assumes the link MTU of the interface from which the traffic is being forwarded and then sends the IPv6
packet at the link MTU size. If a router on the path is unable to forward the packet, it sends an ICMP
Packet Too Big message back to the sending node containing the link MTU of the link on which the packet
forwarding failed. The sending node then rests the PMTU to the value of the MTU field in the Internet
Control Message Protocol version 6 (ICMPv6) Packet Too Big message, and the packet is resent.
The MTU for IPv6 packets can be set on a per-interface basis. There are two methods for setting MTUs for
interfaces if required: one for Layer 3 interfaces, and one for the underlying Layer 1 and Layer 2 interfaces.
For all interface types, use the ipv6 mtu <size> command to specify the IPv6 MTU in bytes from the
interface's configuration mode. The minimum MTU setting for IPv6 is 1280 bytes, and the maximum is
1500 bytes. The IPv6 MTU value is independent of the IPv4 MTU setting (set with the command
<size> on page 2631).
When the interface is forwarding the IPv6 packet as a router, if the packet size exceeds the IPv6 MTU of
the egress interface, the packet is dropped and ICMPv6 Packet Too Big message is sent to the source.
When originating an IPv6 packet from the local IPv6 stack, and the packet is larger than the IPv6 MTU of
the egress interface, the packet is fragmented and sent.
Usage Examples
The following example specifies the IPv6 MTU value for the interface:
(config)#interface tunnel 1
(config-tunnel 1)#ipv6 mtu 1350
60000CRG0-35E
Specifies the MTU value. Valid range is 1280 to 1500 bytes.
Command was introduced.
Command was expanded to include the tunnel interface.
Copyright © 2012 ADTRAN, Inc.
Tunnel Interface Command Set
ip mtu
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